Report: Volume Of New Dengue Cases Close to 400 Million A Year

The World Health Organization has traditionally estimated that about 50 to 100 million new cases of dengue are discovered every year.

But new research indicates the problem is actually much larger, with estimates now at around 390 million cases annually, nearly four times larger than the previously believed number.

The findings are the result of a new study published online Sunday in the journal Nature.

However, since about two-thirds of those with the tropical illness -- also known as "break-bone fever" -- have only a mild version and don't need medical attention, the data won't change how patients are handled.

Hope remains that the new numbers could prompt a speedier search for a vaccine for the mosquito-borne disease. The study was funded by the Wellcome Trust, the U.S. Department of Homeland Security and others.

The World Health Organization said it wasn't surprised by the higher estimates. "We fully agree the spectrum of dengue is very wide and there was every chance we were missing cases," said Raman Velayudhan, the agency's global dengue coordinator.

The global health agency was not involved in the new research.

"The new numbers are not out of the realm of what was expected," said Jeremy Farrar, director of the Oxford University Clinical Research Unit in Vietnam, one of the study authors. He said the figures came from analyzing more evidence than was used in the past and included other factors that influence dengue.

Dengue causes symptoms including fever and severe joint pains. The disease mostly affects people in Asia, Africa and Latin America though it has also recently popped up in parts of Western Europe and the U.S.

There are four kinds of dengue and catching it once doesn't ensure immunity; subsequent infections raise the risk of severe dengue and may include hemorrhaging. The death rate is usually below 1 percent if patients get treated quickly, but can rise to 10 percent if they're not treated.

Clarence Tam, an infectious diseases expert at the London School of Hygiene and Tropical Medicine, said more research was needed on the significance of the nearly 300 million people who have mild dengue.

"Whether these cases are an important source of dengue infection for others is not well known," he said. "But there is clearly more dengue in the world than we thought."